Process for preparing poly-beta-hydroxybutyric acid



United States Patent Thisinvention relates to the synthesis of poly-[3:hydroxybutyrlc acid, a polymer consisting of repeating units of the formula [CH(CH )CH C(O)O] In one particular aspect it is a method for obtaining greater yields of poly-fi-hydroxybutyric acid without significantly degrading the polymer. In another particular aspect it is a method for obtaining a polymer with valuable properties 7 as a plastic.

In summary, the invention in its broadest aspect is directed to extracting poly-B-hydroxybutyric acid from bacteria containing the same, by means of a solvent containing a hydrolyzing agent.

In my copending application, Serial No. 58,154 filed Sept. 26, 1960, of which this application is a continuationin-part, there is described a method for isolating poly-,8- hydroxybutyric acid by extraction with pyridine. I have now found that a mixture of methylene chloride and ethanol will not only extract about as much polyester as pyridine, but it will also give a product with considerably higher viscosity.

The poly-B-hydroxybutyric acid produced by this novel method is a translucent, plastic-like material which can be utilized in several ways. It is easily cast into a film or molded into articles by conventional methods. It is also useful for surface coatings and as a fiber. It is especially useful in the field of medicine. Medical sutures made of poly-fl-hydroxybutyric acid need not be removed since they eventually decompose to naturally occurring substances without harm to the patient. Films of poly-p-hydroxybutyric acid can be used to support injured arteries and blood vesselsuntil the tissues heal.

Poly-fl-hydroxybutyric acid can be synthesized by various bacteria under suitable conditions. The choice of bacteria depends not only on one capable of forming this polyester, but also on one which can effect the desired biochemical change within a relatively short time and can produce the highest yield with a minimum of attention.

The families where this polyester-is known to be a major constituent include Athiorhodaceae, Pseudomonadaceae, Spirillaceae, Rhizobiaceae, Bacillaceae and Azotobacteriaceae. Rhodospirillum rubrum of the Athiorhodaceae family and Bacillus megaterium of the Bacillaceae family are notable examples. Cultures of bacteria used in established processes are usually available from scientific culture collections such as the A.T.C.C. (American Type Culture Collection, Georgetown University, School of Medicine, Washington, D.C.), the collections of various universities and the U.S. Department of Agriculture.

The individual bacteria cells are physiologically independent. A thin membrane determines the outside bound ary of the cell and constitutes the cell wall. Within the cell is a colloidal solution known as cytoplasm. Some of the granules suspended in the cytoplasm have been found to be composed largely of poly-,B-hydroxybutyric acid. Under appropriate conditions unusually large amounts of this polyester can be built up in the cells.

There are two processes presented in the literature for isolating poly-fi-hydroxybutyric acid from bacteria. In one process the polyester is extracted from the dried bacterial cells with chloroform. Although this method gives a polymer with useful properties as a plastic, the yield'is other alcohols, carboxylic acids and amines. these compounds when present in small amounts will much too low for this process to be of any value. In

order to increase product yields, a second method was devised whereby the dried bacterial cells are first digested in sodium hypochlorite and'the resulting insoluble residue, crude poly-,G-hydroxybutyric acid, is extracted with chloroform. The product obtained by this second method is so degraded that, it is useless as a plastic.

It is, therefore, an, object of this invention to provide an improved process for producing greater product yields of poly-,B-hydroxybutyric acid without significantly degrading the polymer than methods heretofore employed.

It is a further object of this invention to produce a polymer with valuable properties as a plastic.

It has been found that yields of poly-fl-hydroxybutyric acid are greatly increased by extracting the polyester with a solution of a solvent and a mild hydrolyzing agent.

It has also been foundthat the bacteria cells are sufficiently broken up by dispersing them in acetone.

To carry out this improved process, large quantities .of appropriate bacteria are grown in a suitable nutrient medium. .The bacteria are collected by known means, e.g., centrifugation, and the mass of wet cells is dispersed in' acetone. A cellszacetone weight ratio of 1:1 to 10 is suitable. i

In addition to breaking up the cell walls, the acetone removes water and dissolves lipids and other materials which would otherwise contaminate the product. The use of acetone at this stage makes the polyester readily ex tractable.

The acetone is removed and the bacterial residue is The powder is treated with a Methylene chloride asa solvent with ethanol as residuenn'ethylene chloride/ ethanol solution weight ratio of about 1:10 to is used. The bacterial residue pow. der can be treated with the methylene chloride/ethanol solution at reflux temperature or below.

The polyester solution is filtered and the polyester can be recovered from the filtrate by various methods. The polyester can be recovered by evaporating the solution.

Suitable precipitants such as petroleum ether and petroleum hydrocarbons in general can be used. A means that is particularly suitable for precipitating the polyester,

and which is a preferred embodiment of this invention, is

to add ether to the'methylene chloride/ ethanol solution. An etherzmethylene chloride/ethanol ratio of about 3:1 is suitable.

Other methods of recovering the polyester include adding water, alcohol and nonpolar solvents such as benzene Mixing the cell mass with an antioxidant and placing it in an oven at about C. is another method.

Obviously, other solvents such as chloroform, 1,4- dioxane or pyridine can be used as the polymer solvent 7 in place of methylene chloride. I

Other hydrolyzing agents which can be used include Any of break a few of the'polyester bonds and thus reduce the Patented'July 17, 1962 average molecular weight of the polyester enough to make it dissolve.

The following examples will serve to illustrate the invention:

This data illustrates the effect of a hydrolyzing agent. Methylene chloride, alone, extracted only a negligible amount of polyester as compared to that extracted by the methylene chloride/ ethanol solution. The methylene EXAMPLE I chloride and triethanolamine mixture extracted an unusually large amount of polyester even though a large A nutnenmedmm havmg the followmg composition amount of quaternary ammonium salt was also produced was Prepare under these conditions. Glucose g 240-0 EXAMPLE 1v Mineral solutions 500-0 Yeast extract g 9.0 A nutrlent medium havlng the followlng composmon Water ml 12000.0 was prepared:

Mineral solution: 10.0 g. (NH4)2SO1, 10.0 KHgPOl, p hate -1 3200 -HP-7 .2. .Ms0,o.2.ch12,o.o6. 1 i it ilfio ddfo mg m di 0 g g 4 g a g Mixed mineral SOllltlOn ..ml 320.0 Th nutrient medium was autoclaved and allowed to Sodmm acetate 1, A 500 m1. inoculum of Bacillus megaterium Yeast extract ,c c #3245 from a 24-hour old culture was added Water to the nutrient medium. The medium was continuously 1 Phosphate bu -0 g- KH2P04, NMHPOPTHQO,

d t t ature for about sixt hours with 2000 {111' firm d a 1 1! p f' b 200 500 Y t l ltgxedfilglguera solutll i i: l0 tg nltliltfillflcegii gacld gl si tere air att e rate 0 a out to cc. per mlnu e. S0 ve in a Ben m 29 W so \1 0n 0 Aeration was vigorous enough to mix the nutrient medil%.ffi3 fi gfiighfig? gj fiifigdi g d um continuously. At the end of the incubation period, tl tcg m etgl solution. It Add H20 to give 1 and adjust to h lls w re harvested y centfifugafion and mixed With p Sthhdal'd trace metal solution: 0.106 g. COCOa, 1.14 200 ml. of acetone. The acetone was filtered off and the a i fl m gi g ggg g 'ggf gg fig ggf bacterial residue was added to another 200 ml. of acetone h i E 1 P and allowed to stand for about 15 hours. The acetone Th di 1 d d n d was then removed and the bacterial residue was air dried 1 e Ri g? um as a g to until the odor of acetone disappeared. The dried residue m mocu um of um van Weighed 11.4 30 Niel strain 1.1.1.) from a seven day old culture was added to the nutrient medium. Two 150-watt fioodlights were EXAMPLE H focused on the culture and the temperature was manone gram 9 y megalerlllm c6113 p l 111 the tained at about 30 C. The medium was continuously ma le described In EXamPIe I Was added l y to aerated with a stream composed of 5% N and 95% CO solution consisting of 50 ml. of methylene chlorlde and Aft r i d h Stream of N d CO was stopped 10 ml. of ethanol. The solution was refluxed for 10 mm- D d h culture was t d ith H f i h Th utes and filtered. 2Q). ml. of ether was added i0 1116 H rose from 7 to 9 The Hz was stgpped and aeration clear filtrate 0 p p t the p y After three with N and CO was resumed for 18 hours and then hours the solution was chilled, filtered and the polyester Stopped. Aeration with H was resumed and after 6 precipitate was dried in a vacuum dessicator. The dried hours h H was stopped Th ll were ha ve ted product weighed 0.173 g. by centrifugation and weighed 37.6 g.

EXAMPLE HI EXAMPLE V Samples of dry B. megaterium produced in the manner The elfectiveness of various solvents in extracting polydes n Example I were placed 1n solvents as list B-hydroxybutyric acid is illustrated in the table below. below. Each sample was filtered and 200 m1. ether Was The degree of polymerization of the final product is indiadded to each filtrate to precipitate the poly-fi-hydroxycated by the intrinsic viscosity. R. rubrum cells obtained butyric acid. After about fifteen hours each sample was in Example IV were used.

Sample No. R. rubrum cells Solvent Time Temp. Yield a a t Cells, g.

1 Dried (1.7g. ml. Pyridine 15 R n .22 1. 2 1o 50111101101. ZOEiEHHUElO L iN 3.135% 3.3% 88% 3 do 5oetirllifiolCHzclz-l-l0 ml. 41 days 30 0..-- 0.23011 2.20 0.401 4 e (7-50g.)---- gg 1CHzCh+10 ml. 5% days... 30C---. 0.115 1.90 0.152 5 do 50 ml. 0121 or d e s Wet (5.6 g.).. 50 1111. 011 013 13 Z3 3 lil IIIIIILIII 1 From 5.0 g. of wet cells.

filtered. Samples A and B were air dried while samples C, D and B were washed with water several times before being air dried.

EXAMPLE VI 3 g. of wet R. rubrum cells were dispersed in acetone and allowed to stand at room temperature for three hours. The acetone was filtered oil and the bacterial mass was air dried. The dried bacterial mass was dissolved in a solution of ml. of methylene chloride and 20 ml. of ethanol. The cells were filtered off and the clear filtrate was placed in a flat dish to dry slowly in the air. After all the solution had evaporated, a thin translucent film remained. The film was easily peeled from the dish.

To determine the type of product obtained when the bacterial mass is initially digested in sodium hypochlorite solution, 3 g. of wet R. rubrum cells were dispersed in sodium hypochlorite solution and allowed to stand at room temperature for three hours. The solution was filtered off and the bacterial mass was air dried. The same procedure was then followed as described above. After all the solution had evaporated, a greyish-white material remained which crumbled easily.

EXAMPLE VII 5 g. of R. rubrum cells producedin the manner described in Example IV, were mixed with 4 mg. of 2,6- di tertiary-butyl-4-methyl-phenol and dried in an oven at 105 C. The dried sample, weighing 1.7 g., was dispersed in a solution of 50 ml. of methylene chloride and ml. of ethanol and allowed to stand at 30 C. After four days the solution was filtered and 200 ml. of ether was added to the clear filtrateto precipitate the polyester. After three hours the solution was chilled, filtered and the polyester precipitate was dried in a vacuum dessicator. The dried product weighed 0.21 g.

EXAMPLE VIII The procedure of Example VII was followed except that the bacterial cell mass was dried in an oven at 105 C.

for six hours in the absence of oxygen before dispersing in methylene chloride/ ethanol solution.

EXAMPLE IX The procedure of Example VII was followed except that the bacterial cell mass was dried in a vacuum (650 mm. Hg) for 16 hours before dispersing in methylene chloride/ ethanol solution.

I claim:

1. In the process of preparing poly-fi-hydroxybutyric acid by the growth of bacteria in a culture medium whereby the bacteria acquire deposits of said polyester within their cell walls followed by recovery of the polyester-bearing bacteria and the solvent extraction of the polyester from the bacteria, the improvement comprising the steps of dispersing the polyester-bearing bacteria in acetone to break up the bacteria cell walls and to remove lipids and water therefrom, separating the thus treated bacterial residue and dispersing it in a methylene chloride/ethanol solution to cause mild partial hydrolysis of poly-B-hydroxybutyric acid and to extract it from the bacterial residue, separating the insoluble bacterial residue from the methylene chloride/ethanol solution, and recovering the poly-B-hydroxybutyric acid from the methylene chloride/ ethanol solution.

2. The method according to claim 1 in which the poly- B-hydroxybutyric acid is recovered from the methylene chloride/ethanol solution by adding liquids miscible with methylene chloride thereto to precipitate the polyester.

3. The method according to claim 1 in which the methylene chloridezethanol weight ratio is substantially 1:1 to :1.

4. The method according to claim 1 in which the poly- B-hydroxybutyric acid is recovered from the methylene chloride/ethanol solution by adding ether thereto to precipitate the polyester.

5. The method according to claim 1 in which the bacteria is selected from the group of families consisting of Anthiorhodaceae, Psuedornonadaceae, Spirillaceae, Rhizobiaceae, Bacillaceae and Azotobacteraceae.

6. The method according to claim 5 in which the bacterium is Bacillus megaterium.

7. The method according to claim 5 in which the bacterium is Rhodospirillum rubrum.

8. The method according to claim 1 in which the weight ratio of bacteriazacetone is substantially 1:1 to 10.

9. The method according to claim 8 in whichthe weight ratio of bacterial residuezmethylene chloride/ethanol is substantially 1:10 to 100.

10. The method according to claim 9 in which the extraction with methylene chloride/ ethanol solution is carried out under reflux for about 5-30 minutes.

11. The method according to claim 10 in which ether between about 1:1 and 10:1, whereby poly-fl-hydroxybutyric acid is precipitated, followed by recovering and drying the said precipitate.

12. The process of recovering poly-fi-hydroxybutyric acid from a bacterial cell mass containing this polyester w which comprises adding the bacterial cell mass to methylene chloride/ethanol solution to extract the poly- 8- hydroxybutyric acid, separating the methylene chloride/- ethanol/polyester solution from the cell residue, and recovering the polyester product from solution.

:13. The process of preparing poly-p-hydroxybutyric acid which comprises growing appropriate bacteria in a culture medium under conditions conductive to the formation of poly-,B-hydroxybutyric acid, adding the bacterial cell mass to methylene chloride/ethanol solution to extract the poly-B-hydroxybutyric acid, separating the methylene chloride/ethanol/polyester from the cell residue, and recovering the polyester product from solution.

14. The processlof recovering poly-B-hydroxybutyric acid from a bacterial cell mass containing this polyester which comprises drying the bacterial cell mass, dispersing it in methylene chloride/ethanol solution to extract the poly-,S-hydroxybutyric acid, separating the methylene chloride/ethanol/polyester solution from the .cell residue, and recovering the polyester product from solution.

15. The method according to claim 14 in which the bacterial cell mass is dried by extracting it with acetone.

16. The method according to claim 14 in which the bacterial cell mass is dried in an oven at 105 C. in the absence of oxygen.

17. The method according to claim 14 in which'the bacterial cell mass is mixed with an antioxidant and dried in an oven at about 105 C.

18. The method according to claim 14 in which the.

bacterial cell mass is dried under a vacuum.

19. The process of preparing poly-fl-hydroxybutyric acid from Rhodospirillum rubrum by inoculating Rhodospirillum rubrum into a culture medium comprised of 320 1111. phosphate buffer composed of 46.0 g. KH PO 86.4 g.

standard trace metal solution, enough H O to make 1 l.

' adjusting pH 6.5 to 7.0, the standard trace metal solution being composed 0.106 g. CoCO 1.14 g. MnCO 5.21 g. ZnCl 5.0 g. FeSO -7H O, 0.39 g. CuSO -5H O; 0.117 g. H BO 2.50 g. versene acid, several drops H SO 1000.0 ml. H O; aerating the inoculated culture medium with a nitrogenzcarbon dioxide mixture under illumination; stopping the nitrogenz-carbon dioxide flow and aerating with hydrogen under illumination; harvesting the bacterial cell mass; dispersing the bacterial cell mass in acetone to break up the bacterial cell walls and to remove lipids and water therefrom; separating'the thus treated bacterial cell mass and dispersing it in methylene chloride/ ethanol solution to extract poly-,B-hydroxybutyric acid; separating the polyester solution from the cell residue; adding ether to the polyester solution to precipitate the polyester and recovering the polyester product.

20. The process of preparing poly B hydroxybutyric acid from Bacillus megaterium. by inoculating Bacillus megaterium into a culture medium comprised of 240 g. glucose, 9 g. yeast extract, 600 ml. mineral solution and 12,000 ml. water, the mineral solution being composed of 10 g. (NH SO 10 g. KH PO 18.9 g. Na HPO -7H O, 2 g. MgSO 0.2 g. CaCl 0.06 g. FeCl and 1000 ml. H O; continuously aerating the inoculated culture medium during the incubation period with filtered air at about room temperature during the incubation period; harvesting the bacterial cell mass; dispersing the cell walls and to remove lipids and water therefrom; separating the thus treated bacterial mass and dispersing it in methylene chloride/ethanol solution to extract poly- S- hydroxybutyric acid; separating the polyester solution from the cell residue; adding ether to the polyester solution to precipitate the polyester and recovering the polyester product.

21. The process of recovering poly-B-hydroxybutyric acid from a bacterial cell mass containing this polyester by drying the bacterial cell mass under nonoxidative conditions, dispersing it in a poly-B-hydroxybutyric acid solvent/hydrolyzing agent solution to cause mild partial hydrolysis of the polyester and to dissolve the polyester, separating the solution of polyester from the cell residue, and recovering the polyester product from the solvent/ hydrolyzing agent solution.

No references cited.

i UNITED STATES PATENT OFFICE CERTIFICATF. OF CORRECTION Patent No; 3,044,942 July 17, 1962 James Noel Baptist It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 45, for "CaC read CaC1 Signed and sealed this 8th day of January 1963,

( SEAL) Attest:

ERNEST w. SWIDER VID L- L Attesting Officer Commissioner of Patents 

13. THE PROCESS OF PREPARING POLY-B-HYDROXYBUTYRIC ACID WHICH COMPRISES GROWING APPROPRIATE BACTERIAL IN A CULTURE MEDIUM UNDER CONDITIONS CONDUCTIVE TO THE FORMATION OF POLY-B-HYDROXYBUTYRIC ACID, ADDING THE BACTERIAL CELL MASS TO METHYLENE CHLORIDE/ETHANOL SOLUTION TO EXTRACT THE POLY-B-HYDROXYBUTYRIC ACID, SEPARATING THE METHYLENE CHLORIDE/ETHANOL-POLYESTER FROM THE CELL RESIDUE, AND RECOVERING THE POLYESTER PRODUCT FROM SOLUTION. 